1. Field of the Invention
The present invention refers to a micro-electro-mechanical structure having electrically insulated regions and the manufacturing process thereof. In particular, the present description makes reference to of micro-integrated gyroscopes, without, however, being limited to these.
2. Description of the Related Art
As is known, integrated gyroscopes of semiconductor material, manufactured using micro-electro-mechanical-systems (MEMS) technology, operate on the basis of the theorem of relative accelerations, exploiting the acceleration of Coriolis. In particular, when a linear velocity is applied to a mobile mass rotating with angular velocity, the mobile mass “senses” an apparent force, called Coriolis force, which determines a displacement thereof in a direction perpendicular to the linear velocity and to the axis of rotation. The apparent force can thus be detected by supporting the mobile mass on springs, which enable a displacement thereof in the direction of the apparent force. On the basis of Hooke's law, the displacement is proportional to the apparent force, and thus detection of the displacement of the mobile mass enables detection of the Coriolis force and consequently of the angular velocity.
In gyroscopes of the type considered, the displacement of the mobile mass is detected capacitively by measuring at resonance the variations in capacitance caused by the movement of mobile sensing electrodes fixed to the mobile mass and interfaced with or comb-fingered to fixed sensing electrodes.
An embodiment of an integrated gyroscope manufactured using planar MEMS technology is, for example, described in U.S. Pat. No. 6,766,689, issued in the name of the present applicant. This integrated gyroscope is formed by an actuation assembly; a sensitive mass, which is actuated in a first direction lying in the plane of the sensitive mass and is moreover mobile in a second direction, which also lies in the plane of the sensitive mass; and a capacitive sensing system facing the sensitive mass and capable of detecting the movements thereof in the second direction. The gyroscope has an axis of rotation perpendicular to the plane of the sensitive mass so that, in presence of an external angular velocity, the sensitive mass moves in the second direction.
Another patent application in the name of the present applicant (U.S. patent application Ser. No. 10/685,292) describes a gyroscope capable of detecting the Coriolis force even when this acts in a direction perpendicular to the plane of the sensitive mass.
To obtain high performance and prevent cross-talk between actuation and reading of the signal, it is desirable to bias at different voltages the actuation assembly and the sensitive mass, at least in the part facing the capacitive sensing system.
Since in current gyroscopes made as MEMS, the two mechanical blocks are formed in a same structural layer (polysilicon layer), it is necessary to uncouple them electrically by insulating regions.
The same problem is present, on the other hand, in other MEMS, for example in accelerometers, where it may be necessary or at least preferable to electrically separate two suspended adjacent parts.